基于SPI/SPEI指数的东北地区多时间尺度干旱变化特征对比分析

利用东北地区(黑龙江、吉林、辽宁)1960—2014年90个气象台站的逐日地面观测数据(平均气温、降水量、日照时数、平均相对湿度、平均风速及平均水汽压),利用标准化降水指数(SPI)和标准化降水蒸散指数(SPEI),对比分析近55 a多时间尺度干旱变化特征及两指数的表征差异。(1)依据各气象台站年总降水量,可将东北地区分为5个子区,各分区年总降水量皆未表现出显著的长期趋势,但Ⅰ、Ⅱ、Ⅳ区和Ⅴ区年总潜在蒸散量分别呈现显著下降、上升趋势。(2)两指数在1个月(1 mo)尺度上围绕0值频繁波动,随时间尺度增加,形成干湿阶段持续期,其中干旱期持续时间较湿润期稍长。不同时间尺度二者评估旱涝结果总体相似,其中短时间尺度,SPI较SPEI易受降水影响,波动大。长时间尺度差距减小,但在判别程度上SPI较SPEI偏轻。在特殊干旱年1982年和1999年,SPI在降水量减少幅度较大地区或月份监测干旱能力下降。(3)SPI描述东北地区无旱及特旱发生频率时较SPEI高,中旱、重旱及湿润发生频率则相反。(4)在评估东北地区旱涝情况时SPEI指数较SPI指数适用性更好。     

渭河流域多尺度干旱时空特征分析

基于渭河流域23个气象站1959—2014年的实测资料,对比分析了标准化降水指数(SPI)和标准化降水蒸散指数(SPEI)在渭河流域的适用性,得出SPEI的稳定性更佳。继而采用标准化降水蒸散指数(SPEI)研究该流域干旱发生频率与干旱强度,分析了近55年渭河流域不同时间尺度干旱的时空变化特征。结果表明:尺度越大,SPEI波动的幅度越小。渭河流域SPEI在1991年发生突变,1991年后干旱加剧,干旱的发生存在14 a和7 a左右周期变化。年尺度干旱的发生频率呈东高西低的分布,中度以上干旱频率最高的地区为西吉、武功和天水周边,频率分别为14.28%、14.28%、12.5%;季尺度上整体的秋旱相比其它季节的干旱发生频率高,中度以上春、秋、冬三季干旱发生的频率天水盆地均最高,频率分别为21.4%、19.6%和8.9%,中度以上夏季干旱发生频率最高的是平凉,其频率为16.1%;月尺度上干旱强度的分布总体上是由东向西减小,其中干旱强度最大的是南部佛坪地区,干旱强度为30%,天水和海源地区近55年发生连续干旱过程的次数最多,可达22 a,该过程中连续干旱的月数大多为3~4个月,而吴旗站存在一次长达9个月的持续干旱过程。     

4种干旱指标在华北地区气象干旱监测中的适用性分析

采用华北地区1961—2016年69个气象站点常规观测资料，通过选取特殊气象代表站点，选用CI、SPEI、SPI及Z指数分别计算了1、3、12个月时间尺度气象干旱，并与气象干旱发生实况进行对比分析。结果表明：（1）CI计算的华北地区不同区域各时间尺度气象干旱发生频率均较实际明显偏高7%~14%，Z指数计算的发生频率均较实际明显偏低6%~12%，SPI计算的部分区域季时间尺度气象干旱发生频率也明显偏低6%左右；（2）根据华北地区9个代表气象站点计算出的4种干旱指标对比干旱发生实况统计数据，结果显示在4个研究分区中，SPEI指数表征的干旱发生状况与实际吻合率最高，分别为57.41%、60.78%、57.06%和66.99%，与实际干旱发生状况吻合程度最低的是Z指数，4个研究分区的吻合率分别为40.85%、34.94%、41.56%和38.24%。研究表明，SPEI表征各种时间尺度气象干旱发生效果最好，Z指数效果最差。因此，选用SPEI能较准确地表征华北地区气象干旱年际变化及突变检测、时间分布、空间分布、干旱发生强度、不同等级干旱分布等特征。     

贵州省干旱时空分布特征研究

为探究季节性干旱对贵州省农业生产造成的影响,基于贵州省9个气象站点1960~2010年逐日降雨资料计算的标准化降水指数(SPI),使用Mann-Kendall趋势检验和GIS克里金插值等方法,分析了该区域近51a以来的干旱时空分布特征。结果表明:近51a来贵州省内大部分站点的月尺度SPI值在4-5月和9-10月呈下降趋势;年尺度SPI值呈减小趋势,干旱影响站次比呈上升趋势,干旱范围和干旱程度有加大趋势;1年四季中干旱频率空间分布在不同地域上显示出了较大差异性。     

基于SPEI和时空立方体的中国近40年干旱时空模式挖掘

利用1980—2019年中国612个气象站点逐月降水量和温度数据计算多尺度标准化降水蒸散指数(SPEI),根据中国气温条件划分7大地理分区并结合时空立方体、时空热点分析、时空聚类和时空异常值来探究中国近40年多尺度标准化降水蒸散指数SPEI的时空分布特征。结果表明:(1)通过干旱频率的计算,发现轻度干旱和极端干旱最为严重的地区为内蒙古草原地区,严重干旱和中度干旱在西北荒漠地区最为严重。(2)通过时空立方体展示出中国旱情在时空分布上差距较为显著,西北地区最为严重,其次是西南的西部地区和华北的北部地区;(3)对我国近40年SPEI 12的时空热点进行分析可得我国旱情的时空趋势,其中冷点地区和热点地区各有2个,热点主要分布在华中和东北地区的西部,冷点主要分布在华中的中部地区;4)对多尺度SPEI进行局部异常值分析得到,年尺度的华南西部和华中、华南湿润亚热带地区的中部呈低-低聚类,说明该地全年旱情相对更严重。     

基于多源遥感数据的温度-土壤湿度-降水干旱指数(TMPDI)的构建与应用

干旱在全球范围内产生了深远的社会和经济影响,可靠的干旱监测对防旱抗旱工作具有重要指导意义。由于在植被覆盖度和农作物种植率较低区域使用植被状态或单因子进行干旱监测时精度较低,故本文采用地表温度(LST)、降水量(P)和土壤湿度(SM)数据,基于三维欧氏几何空间中欧氏距离方法构建了一种新的干旱指数:温度-土壤湿度-降水干旱指数(TMPDI)用于干旱监测。并以甘肃省为研究区,利用SPI、SPEI、遥感数据以及小麦单位面积单产对TMPDI进行验证。结果表明:TMPDI与SPI、SPEI高度相关(R20.64),且在干旱监测中兼顾降水量与气温影响的同时,降低了使用降水量或地表温度进行干旱监测的不确定性,提高了土壤湿度在农业干旱监测中的准确性与有效性,能准确地描述干旱事件的时空演变特征,同时也能较好地反映出干旱强度与干旱面积率的变化对小麦产量造成的影响,说明TMPDI在农业干旱监测中具有较高的有效性和可靠性。     

PDSI和Z指数在西北干旱监测应用中差异性分析

利用西北地区137个气象台站1961～2003年气象资料,分别计算了西北地区的Z和PDSI两种干旱指数,并对其结果进行了对比分析.结果认为:两种指数在多数地区多数季节可以互相兼容,但Z指数适宜于在雨季表征干湿事件,而PDSI则适宜于西北的所有地区和所有季节,并对当地干旱事件的反映更为敏感;在对不同程度干旱面积的表征上,PDSI对轻旱的表征反映较为敏感,而Z指数对重旱的反映更为敏感;对于中等程度的干旱而言,两种指数表征下的干旱面积较为统一;从西北地区的实际情况出发,PDSI对干旱的表征更为客观.     

1961—2012年我国干旱演变特征

利用气象观测数据、气象干旱指数及Mann-Kendal统计检验方法,研究我国近52 a的旱情特征及旱情变化趋势,基于标准化降水蒸散指数SPEI评估不同区域旱灾发生次数、频率及覆盖面积等。结果表明：当时间尺度较小时,SPI指数与SPEI指数变化频率快,这两种指数都能有效地反映出区域旱情信息,而SPEI指数旱情监测效果更好;全国绝大部分站点降水量呈现下降趋势,但没达到显著水平;绝大部分站点平均气温呈现显著上升趋势,且SPEI值也表现出干旱趋势;全国不同省份发生旱灾的频率差异性大,河北、黑龙江、湖北、贵州和宁夏5省份在2001—2010年遭受的旱灾次数高于其他时期,大部分省份干旱覆盖面积呈现显著增大趋势。     

基于标准化降水指数与Z指数的洮河流域干旱趋势分析

采用洮河流域22个站点1951-2010年的逐月降水资料,就标准化降水指数(standardized precipitation index,SPI)与Z指数在流域干旱趋势分析中的应用进行对比研究.结果表明:2种指数在12个月尺度旱情分析方面具有很高的一致性,在单月尺度上,SPI的干旱分析能力较强,对重旱的反映能力优于Z指数.应用SPI指数就洮河流域不同地理—生态区间干旱趋势进行研究,发现冬季是流域干旱的主要分布时段,黄土片区发生干旱的频率和持续的时间均高于青藏片区.1951-2010年,青藏片区总体趋于湿润,黄土片区干旱趋势加重.近30 a,洮河青藏片区西部湿润趋势明显,东南部和下游黄土片区干旱趋势加重.近10 a来,青藏片区东南部旋窝一带干旱范围有所减小,黄土片区中孚一带干旱范围有所扩大.研究结果可为大流域尺度干旱评估提供理论方法借鉴,也可为地方抗旱减灾措施的制定提供数据支撑.     

基于SPI的近51a晋北地区旱涝变化及干旱事件时空特征研究

利用晋北地区1965-2015年逐月降水数据,计算不同尺度标准化降水指数(SPI),并结合游程理论,分析了晋北地区旱涝变化及不同时间尺度干旱事件时空演变特征。结果表明:晋北地区呈湿润化演变趋势,年SPI以0.0507/10a的速率递增,春、秋、冬季变湿,对年湿润化过程的贡献明显。就干旱事件而言,干旱持续时间、干旱程度和干旱强度均呈递减趋势,晋北地区干旱事件缺水状况有所缓解;1965年气象和农业干旱最严重,1999-2000年水文干旱最严重;河曲是农业和水文干旱的高发区,干旱化趋势也最为明显,五寨呈明显的湿润化趋势,其气象干旱最严重。     

Performance of different drought indices for agriculture drought in the North China Plain

The Palmer drought severity index(PDSI), standardized precipitation index(SPI), and standardized precipitation evapotranspiration index(SPEI) are used worldwide for drought assessment and monitoring. However, substantial differences exist in the performance for agricultural drought among these indices and among regions. Here, we performed statistical assessments to compare the strengths of different drought indices for agricultural drought in the North China Plain. Small differences were detected in the comparative performances of SPI and SPEI that were smaller at the long-term scale than those at the short-term scale. The correlation between SPI/SPEI and PDSI considerably increased from 1-to 12-month lags, and a slight decreasing trend was exhibited during 12-and 24-month lags, indicating a 12-month scale in the PDSI, whereas the SPI was strongly correlated with the SPEI at 1-to 24-month lags. Interestingly, the correlation between the trend of temperature and the mean absolute error and its correlation coefficient both suggested stronger relationships between SPI and the SPEI in areas of rapid climate warming. In addition, the yield–drought correlations tended to be higher for the SPI and SPEI than that for the PDSI at the station scale, whereas small differences were detected between the SPI and SPEI in the performance on agricultural systems. However, large differences in the influence of drought conditions on the yields of winter wheat and summer maize were evident among various indices during the crop-growing season. Our findings suggested that multi-indices in drought monitoring are needed in order to acquire robust conclusions.     

典型干旱指数在滦河流域的适用性评价

利用1957-2010年滦河流域9个代表气象站逐月降水量资料及滦河三道河子、韩家营、承德、下板城和滦县站的1956-2000年逐月天然径流量资料,分别应用降水距平百分率、标准化降水指数（SPI）、降水Z指数及径流距平百分率,评价滦河流域干旱情况,并比较4种干旱指数的评价效果。结果表明：降水距平百分率反映干旱程度较轻;与降水Z指数相比,SPI指数能较客观地反映滦河流域干旱程度,3种气象干旱指数在滦河流域的适用性评价结果SPI]指数优于降水Z指数和降水距平百分率;而径流距平百分率的水文干旱指数评价结果与实际旱情更为吻合。但是,这4种干旱指标缺乏综合性和机理性,尚需加强降水、气温、蒸发、径流量等因素的综合考虑,提出反映干旱内在机理的指标。     

Meteorological drought in semi-arid regions: A case study of Iran

Drought occurs in almost all climate zones and is characterized by prolonged water deficiency due to unbalanced demand and supply of water, persistent insufficient precipitation, lack of moisture, and high evapotranspiration. Drought caused by insufficient precipitation is a temporary and recurring meteorological event. Precipitation in semi-arid regions is different from that in other regions, ranging from 50 to 750 mm. In general, the semi-arid regions in the west and north of Iran received more precipitation than those in the east and south. The Terrestrial Climate (TerraClimate) data, including monthly precipitation, minimum temperature, maximum temperature, potential evapotranspiration, and the Palmer Drought Severity Index (PDSI) developed by the University of Idaho, were used in this study. The PDSI data was directly obtained from the Google Earth Engine platform. The Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) on two different scales were calculated in time series and also both SPI and SPEI were shown in spatial distribution maps. The result showed that normal conditions were a common occurrence in the semi-arid regions of Iran over the majority of years from 2000 to 2020, according to a spatiotemporal study of the SPI at 3-month and 12-month time scales as well as the SPEI at 3-month and 12-month time scales. Moreover, the PDSI detected extreme dry years during 2000-2003 and in 2007, 2014, and 2018. In many semi-arid regions of Iran, the SPI at 3-month time scale is higher than the SPEI at 3-month time scale in 2000, 2008, 2014, 2015, and 2018. In general, this study concluded that the semi-arid regions underwent normal weather conditions from 2000 to 2020. In a way, moderate, severe, and extreme dry occurred with a lesser percentage, gradually decreasing. According to the PDSI, during 2000-2003 and 2007-2014, extreme dry struck practically all hot semi-arid regions of Iran. Several parts of the cold semi-arid regions, on the other hand, only experienced moderate to severe dry from 2000 to 2003, except for the eastern areas and wetter regions. The significance of this study is the determination of the spatiotemporal distribution of meteorological drought in semi-arid regions of Iran using strongly validated data from TerraClimate.     

Response of hydrological drought to meteorological drought in the eastern Mediterranean Basin of Turkey

The hydrographic eastern Mediterranean Basin of Turkey is a drought sensitive area. The basin is an important agricultural area and it is necessary to determine the extent of extreme regional climatic changes as they occur in this basin. Pearson's correlation coefficient was used to show the correlation between standardized precipitation index(SPI) and standardized streamflow index(SSI) values on different time scales. Data from five meteorological stations and seven stream gauging stations in four sub-basins of the eastern Mediterranean Basin were analyzed over the period from 1967 to 2017. The correlation between SSI and SPI indicated that in response to meteorological drought, hydrological drought experiences a one-year delay then occurs in the following year. This is more evident at all stations from the mid-1990 s. The main factor causing hydrological drought is prolonged low precipitation or the presence of a particularly dry year. Results showed that over a long period(12 months), hydrological drought is longer and more severe in the upper part than the lower part of the sub-basins. According to SPI-12 values, an uninterrupted drought period is observed from 2002–2003 to 2008–2009. Results indicated that among the drought events, moderate drought is the most common on all timescales in all sub-basins during the past 51 years. Long-term dry periods with moderate and severe droughts are observed for up to 10 years or more since the late 1990 s, especially in the upper part of the sub-basins. As precipitation increases in late autumn and early winter, the stream flow also increases and thus the highest and most positive correlation values(0.26–0.54) are found in January. Correlation values(ranging between –0.11 and –0.01) are weaker and negative in summer and autumn due to low rainfall. This is more evident at all stations in September. The relation between hydrological and meteorological droughts is more evident, with the correlation values above 0.50 on longer timescales(12-and 24-months). The results presented in this study allow an understanding of the characteristics of drought events and are instructive for overcoming drought. This will facilitate the development of strategies for the appropriate management of water resources in the eastern Mediterranean Basin, which has a high agricultural potential.     

三种气象干旱指标在内蒙古地区的适用性分析

用近五年(2006～2010)内蒙古地区的气象观测资料,对降水距平百分率(pa)、相对湿润度干旱指数(M)和标准化降水指数(SPI)三种气象干旱等级指标的适用性进行了对比分析。发现在作物生长季,pa指标和SPI指数对旱情的评判结果高度一致,而冬春季节则是pa指标和M指数的评判结果比较一致。在多雨季节,可能蒸散量通常比同期降水量小,因此M指数对内蒙古夏季旱情评判等级偏低,不宜使用。同时指出应该将不同时间段干旱影响上的差异,以及干旱灾害的累积效应问题,加入到干旱等级指标的改进中。     

基于TRMM的三江源区8月份干旱特征

以三江源区为试验区,利用1998-2010年热带降雨卫星（tropical rainfall measuring mission,TRMM）和气象站点数据,进行标准化降水指数（SPI）的分析与计算,获得了三江源区8月份10 a干旱变化的时间序列信息,并分析了区域干旱时空变化规律。结果表明：基于TRMM数据的标准化降水指数进行干旱监测精度较好,充分发挥了站点和遥感方法的优势,具有实际应用价值。     

基于加权马尔可夫模型的标准化降水指数干旱预测研究

基于不同时间尺度标准化降水指数的干旱监测结果,以规范化的各阶白相关系数为权重,采用加权马尔可夫链方法对未来干旱状态进行预测和分析.以关中平原和渭北旱塬36个气泉站39年逐月降水量为分析数据.系统地分析了该方法在不同时间尺度(从1个月到1年)上的预测能力及存在的问题.结果表明:对所选的5个时间尺度该方法都有一定的预测能力,并且随着时间尺度的增加,预测正确率也相应提高.同时,该方法对无旱的预测比较准确.对干旱的发生也有一定预测能力,可以作为早期干旱预警的参考.但是,该方法对干旱状态突变的预测能力较弱;随着干旱程度的加重其预测能力也逐渐降低.     

Spatiotemporal analysis of drought variability based on the standardized precipitation evapotranspiration index in the Koshi River Basin,Nepal

Drought is an inevitable condition with negative impacts in the agricultural and climatic sectors, especially in developing countries. This study attempts to examine the spatial and temporal characteristics of drought and its trends in the Koshi River Basin(KRB) in Nepal, using the standardized precipitation evapotranspiration index(SPEI) over the period from 1987 to 2017. The Mann-Kendall test was used to explore the trends of the SPEI values. The study illustrated the increasing annual and seasonal drought trends in the KRB over the study period. Spatially, the hill region of the KRB showed substantial increasing drought trends at the annual and seasonal scales, especially in summer and winter. The mountain region also showed a significant increasing drought trend in winter. The drought characteristic analysis indicated that the maximum duration, intensity, and severity of drought events were observed in the KRB after 2000. The Terai region presented the highest drought frequency and intensity, while the hill region presented the longest maximum drought duration. Moreover, the spatial extent of drought showed a significant increasing trend in the hill region at the monthly(drought station proportion of 7.6%/10 a in August), seasonal(drought station proportion of 7.2%/10 a in summer), and annual(drought station proportion of 6.7%/10 a) scales. The findings of this study can assist local governments, planners, and project implementers in understanding drought and developing appropriate mitigation strategies to cope with its impacts.